I decided to post this since it took me a while to figure it out. (I used the search function)

1. Find the video you want to post.

2. Under the video you will see the Share button:

3. Click it to see the following:

4. Highlight after the v= and right-click, copy:

5. Paste into message portion of your thread:

6. Double-click what you just pasted to highlight it:

7. Click the YouTube button:

8. You will see this:

9. Click 'Submit New Thread'

10. You are done.